The present disclosure relates to optical storage techniques, and more particularly, to duty ratio loops for use in pre-pit detection or header region detection.
In some recordable optical storage media, such as the DVD-R or DVD-RW disc, the physical address information is recorded in the form of pre-pits on the land portions of the disc. The pre-pits formed on the land portions are referred to as land pre-pits (LPPs).
When recording data into a DVD-R/RW disc or reproducing data from the DVD-R/RW disc, the physical address information is obtained by detecting the land pre-pits. In the conventional art, the land pre-pits are detected as follows: Firstly, a push-pull signal is extracted from the DVD-R/RW disc. Then, a slicer is typically employed to slice the push-pull signal on a basis of a predetermined slicing level to generate a binary signal, which is referred to as a land pre-pit signal (LPP signal). According to the LPP signal generated from the slicer, address information of the DVD-R/RW disc and a recording clock signal for use in the recording operation and other similar operations are generated. Accordingly, the pre-pit detecting operation greatly affects the accessing performance of the DVD-R/RW disc.
However, as is well known in the art, the level of the section corresponding to the pre-pit in the push-pull signal is not constant. Conversely, it fluctuates depending on the pickup reading conditions such as the tracking position. Thus, it is difficult to set a proper slicing level for the slicer to slice the push-pull signal.
Differing from the DVD-R/RW disc, the address and location information, such as track and sector numbers, of a DVD-RAM disc are recorded in the header region disposed between adjacent sectors. As is well known in the art, a push-pull signal extracted from the DVD-RAM disc has a rapid signal change in the header region due to a high frequency signal of the header information recorded on the header region.
Reliable detection of a header region is essential to control the rotation of the DVD-RAM disc and is required to precisely read information recorded on a header region.